1. Field of the Invention
The present invention relates to a disc drive servo control apparatus and a method used by the apparatus, and more particularly, to an apparatus to generate an accurate adaptive track zero crossing signal in a disc drive through correction of an offset and unbalance due to a duty correction, although a tracking error signal of the disc drive is offset or unbalanced, and a method used by the apparatus.
2. Description of the Related Art
In general, a transfer speed and position information of a transducer included in a pickup of a disc drive, are estimated using a track zero crossing signal. Thus, if the track zero crossing signal is unstable, the transfer speed and the position information of the transducer cannot be accurately estimated. As a result, a precise seek control cannot be performed.
A general track zero crossing signal generator includes a comparator as shown in FIG. 1. In detail, the tracking error signal (TZCA), which is detected from a pickup and output from an RF amplifier, is applied to a first input node of the comparator, and a reference voltage VREF from a system is applied to a second input node.
However, when an optical spot is transferred at high speed in a direct seek control (unclear), the tracking error signal (TZCA) can be offset or unbalanced due to several reasons such as crossing of optical axes, mechanical friction of a transfer system, noise of the RF amplifier, and slow response of a transfer control system, or impacts. The track zero crossing signal output from the comparator may temporarily be absent in some sections because of the offset or unbalance of the tracking error signal (TZCA). In this case, information on the position and the transfer speed is inaccurate, and thus, malfunction occurs in a seek servo.